The invention relates to internal combustion engines, and in particular, to turbo-charged internal combustion engines with fuel injection rate shaping and internal exhaust gas recirculation.
Emission control standards for internal combustion engines have tended to become more stringent over time. The sorts of emissions to be controlled tend to fall into at least four broad categories: unburned hydrocarbons, carbon monoxide, particulates, and oxides of nitrogen (NOx). Unburned hydrocarbons and carbon monoxide tend to be produced by inefficient or incomplete combustion. Efficient, complete combustion, on the other hand, tends to produce oxides of nitrogen.
Efficient, complete combustion tends to be characterized by high combustion chamber temperatures. The heat associated with high combustion chamber temperatures acts as a catalyst, promoting the binding of oxygen in the air charge to the otherwise inert nitrogen and producing oxides of nitrogen. An engine that is running efficiently, therefore, may produce oxides of nitrogen. Controlling the amounts of emissions produced by an internal combustion engine, then, becomes an issue of balancing combustion efficiency against raising combustion temperatures high enough to produce oxides of nitrogen.
Since the ingredients of oxides of nitrogen come from the intake air, one possibility to reduce the amounts of oxides of nitrogen may be to limit the air available for combustion. Compression-ignition engines, unlike spark-ignition engines, are often run with an excess of air over the stoichiometric ratio, so there is lots of nitrogen available for oxidation. This is because the production of particulates, such as ash, tends to rise as the air/fuel (A/F) mixture approaches stoichiometric. This is evidenced by the observation that diesel trucks often emit puffs of smoke under heavy acceleration. Since compression-ignition engines need to run with an excess of air to avoid emitting particulates, reducing the production of oxides of nitrogen by reducing the amount of air available for combustion is not a practical solution.
Another way to control the production of oxides of nitrogen is to reduce peak combustion chamber temperatures. Since production of oxides of nitrogen tends to depend on high combustion chamber temperatures as a catalyst, reducing the peak temperature ameliorates one of the conditions necessary for the production of oxides of nitrogen. Reducing the peak combustion chamber temperature may thus reduce the amount of oxygen that binds with nitrogen, with a consequent reduction in the quantity of oxides of nitrogen produced.
One means of lowering the high combustion chamber temperatures produced by an efficient combustion event is to cool the combustion chamber during combustion. The combustion chamber may be cooled by, e.g. reintroducing some of the products of previous combustion events back into the combustion chamber, a process known as exhaust gas recirculation (EGR). Since the products of efficient combustion are primarily water and carbon dioxide, neither of which is very flammable, this has the effect of extinguishing the combustion somewhat. The peak temperatures reached in the combustion chamber will consequently be lower, which retards the production of oxides of nitrogen. Clearly, the amount and timing of the introduction of products of combustion must be controlled accurately to avoid impairing the performance of the engine.
Lowering combustion chamber temperatures may have the collateral benefit of reducing exhaust manifold temperatures, as well as stack temperatures. Reducing stack temperatures reduces the temperature in exhaust after-treatment equipment such as oxidation catalysts, with a consequent reduction in the formation of, e.g. sulfates. Reducing stack temperatures may also reduce the production of particulates.
One way to reintroduce some of the products of previous combustion events into the combustion chamber is with external EGR. In external EGR, a tube or plenum conducts some post-combustion gases from the combustion chamber, usually through an exhaust manifold, to a valve. When the valve is opened, the post-combustion gases are readmitted to the combustion chamber, often passing through the intake manifold first. If the post-combustion gases pass through the intake manifold they will mix with fresh make-up air coming in through the air cleaner and be distributed relatively evenly to each of the combustion chambers when its respective intake valve opens.
External EGR, however, relies on high engine heat rejection to work, since the post-combustion gases must travel a relatively long way. Also, the valves and other hardware associated with external EGR increase the cost and complexity of the engine. Furthermore, the addition of external EGR and its associated hardware to an existing engine may require the chassis, front clip, or sheet metal to be re-arranged to allow the engine to fit. Furthermore, if the external EGR is plumbed through the intake manifold, it may be difficult to control the amount of exhaust gas that is re-admitted to each individual combustion chamber. This may pose a problem if, e.g. some combustion chambers run hotter than other combustion chambers, such as those that are nearer the water jacket exit.
A combustion chamber near the exit to the water jacket will be transferring heat to warmer coolant, other things being equal, than a combustion chamber near, e.g. the entrance to the water jacket, since the coolant has already been past the other combustion chambers when it reaches the exit. There will thus be a smaller temperature differential between the combustion chamber and the coolant. Thus the metal around, e.g. the combustion chamber will be maintained at a higher temperature, other things being equal. It would be desirable if the amount of exhaust gas that is readmitted to a combustion chamber could be controlled on an individual basis, commensurate with the temperatures prevailing in that combustion chamber.
The EGR valve, along with the associated actuator and control hardware, is also a point of potential failure, jeopardizing the durability of the engine. It would be desirable if the EGR valve, and its associated actuator and control hardware, could be eliminated. It would further be desirable if the amount and timing of post-combustion gases that re-enter the combustion chamber could be controlled by varying the pressure in the exhaust manifold relative to the pressure in the combustion chamber, rather than with an external valve. Finally, allowing post-combustion gases to re-enter the combustion chamber directly from the exhaust manifold may reduce the transfer time of the post-combustion gases back into the combustion chamber, improving the responsiveness of the EGR system and allowing their application to be optimized or, at least, reduced.
Many truck engines are supercharged. Some superchargers are belt-, chain- or gear-driven, while others, so-called turbo-chargers, rely on a turbine to convert the kinetic energy in exhaust gases to rotational momentum in a compressor. There are those who define superchargers and turbo-chargers as separate entities. For the purposes of this application, however, a turbo-charger will be defined as a turbine-driven supercharger.
Turbo-machinery, such as superchargers, have components that rotate. These components possess inertia. These components gain momentum with respect to this inertia when they are turned, by, e.g. a belt or a turbine. Building rotational momentum requires time, which manifests itself as lag. The lag is generally proportional to the inertia of the turbine rotor and compressor. Thus the inertia of the turbine rotor and the compressor rotor contribute to lag. There are advantages to be found with using smaller compressors and turbine trim, such as better transient engine response, which in turn helps to control emissions, such as, for example, particulates. It would be desirable to be able to reduce the sizes of the turbine and the compressor rotors, thus reducing the lag normally associated with, e.g. turbo-chargers, and improving the transient response.
Turbo-chargers rely on post-combustion gases for their energy. Sometimes, under operating conditions such as at start-up or low-speed operation, an engine does not produce enough post-combustion gases to drive the compressor adequately. It would be desirable if a compressor had a secondary source of power, such as an electrical or belt driven-clutch-assist, for situations when more turbo boost is called for than the available exhaust gas can produce. This would be especially desirable if the turbo-charger were part of the emission control system.
Carnot taught that there are two ways to increase the efficiency of a heat engine, by raising the temperature at which heat is added or by reducing the temperature at which heat is rejected. Although every point within a diesel engine combustion chamber should be at or above the kindling temperature of the fuel when fuel is admitted to the combustion chamber, this may not always be the case. The fuel itself may, e.g. be cold relative to the combustion chamber, especially during winter driving. Cold fuel may thus reduce the temperature locally in the combustion chamber below the kindling temperature of the fuel.
Transient conditions such as those due, e.g. to start up or rapid changes in throttle position may contribute to cooler combustion chamber temperatures as well. Throttling is a cooling process, and so fuel that has been throttled will generally be cooled somewhat. It would be desirable if the fuel being injected were pre-heated slightly by, e.g. using the heat of the post-combustion gases, so that it would be more likely to be ignited completely upon entry into the combustion chamber.
Fuel is normally injected, on the average, into the center of a combustion chamber. Although average combustion chamber temperatures may be relatively constant, local temperatures may fluctuate. Combustion chamber temperatures, for example, may vary both spatially across the combustion chamber, and over time during the combustion event.
Since some points within a combustion chamber are hotter than others, it would be desirable to be able to adjust the rate at which fuel is injected. Thus, the rate at which fuel was injected could be varied at different times and at different points within the combustion chamber, during the combustion event, so fuel was injected where and when the combustion chamber temperatures are highest. This may, for example, allow the combustion process to rely less on propagation of a flame front to burn the fuel. It may also allow the peak temperature to be reduced, thereby reducing formation of oxides of nitrogen, since the fuel can be directed at a point where the temperatures are highest.
Adjusting the rate at which fuel is injected is often termed injection rate shaping. One means of injection rate shaping is described in U.S. Pat. No. 6,336,444 B1 to Suder, the disclosure of which is incorporated by reference. It would be desirable for injection rate shaping to be combined with, e.g., a lash adjustment mechanism, improved turbo-charger efficiency, or in-cylinder exhaust gas recirculation with and without post bump shutoff capability.
In several aspects, the invention may provide post bump shutoff with a lash adjustment mechanism, improved turbo-charger efficiency, a modified post bump injection system, and in-cylinder exhaust gas recirculation with and without post bump shutoff capability. Camless or variable valve timing and lift technologies may be used to shape the post bump to match the region where exhaust port pressure is higher than intake port pressure. In addition, these technologies may provide post bump shutoff capability. Various air systems (shown in FIGS. 5, 6, 7A, 7B, and 11) can be used to overcome lack of airflow (A/F) at low engine speeds with a fixed timing and duration post bump without the shutoff capability.
In one aspect, turbo-chargers may have variable geometry turbines and waste gates. In another aspect, turbo-chargers may be arranged in series. In still another aspect, post bump may be shut off at low engine speeds via, e.g. a lash adjusting mechanism to maintain an acceptable A/F ratio. A conventional turbo-charging scheme (with fixed geometry turbinexe2x80x94see FIG. 8) may also be implemented with shutoff capability. Engine power curves (engine speed and load) may also be manipulated to maintain acceptable A/F at lower engine speeds if the shutoff capability is not available.
In another aspect, the invention provides a combination of in-cylinder EGR and injection rate shaping with a fixed geometry turbo-charger that may be optimally matched for low speed engine operation and good transient response.
In still another aspect, the invention may be a combination of in-cylinder EGR and airflow control via an electrically-assisted turbo-charger, or a variable turbine geometry turbo-charger. Included are injection rate shaping and a turbo-charger that may be optimally matched for low speed engine operation, in addition to a variable turbine geometry turbo-charger and an electrically assisted turbo-charger.
Injection rate shaping may be provided in combination with the specific strategy of in-cylinder EGR. The in-cylinder EGR may be accomplished by, e.g. opening an exhaust valve during the intake stroke, while the exhaust port pulse pressure is greater than the cylinder and intake port pressure. Injection rate shaping may be a combination of pre-, or post-combustion injection rate shaping, and changing a shape of the main injection pulse. Airflow control via, e.g. an electrically assisted turbo-charger, a variable turbine geometry turbo-charger, or a smaller turbine and compressor match may also be included.
In particular, in one embodiment a turbo-charged internal combustion cylinder assembly includes a cylinder having a cylinder head at an end thereof, a combustion chamber with an intake port disposed in the cylinder head, and an intake valve movably disposed in the intake port. The combustion chamber may be communicably connected to the turbo-charger via the intake port so the compressor may provide pre-combustion gases to the combustion chamber when the intake valve is open. An exhaust port is also disposed in the cylinder head, with an exhaust valve movably disposed in the exhaust port that communicably connects the combustion chamber to an exhaust manifold. The exhaust valve may open to exhaust post-combustion gases to the exhaust manifold while the intake valve is substantially closed, and the exhaust valve may open to admit post-combustion gases to the combustion chamber while the intake valve is substantially open. A fuel injector disposed in the cylinder head may admit fuel to the combustion chamber near piston top dead center during, e.g. a compression stroke while both the intake and the exhaust valves are closed. Such a fuel injector may include a pump chamber, a fuel-injecting plunger for reciprocating within the pump chamber, and a discharge nozzle connected to the pump chamber for injecting fuel into the combustion chamber. A spill valve may be positioned between the chamber and the nozzle for controlling a rate of fuel injection to the combustion chamber, the spill valve having a first position providing a maximum fuel injection rate, a second position providing a substantially zero fuel injection rate, and at least one intermediate position providing an intermediate fuel injection rate between the maximum fuel injection rate and the zero fuel injection rate.
In a second embodiment a turbo-charged internal combustion engine system includes a cylinder having a combustion chamber with an intake valve disposed to admit pre-combustion gases to the combustion chamber, and an exhaust port. A first fuel injector may be disposed in the combustion chamber while a second fuel injector disposed in the exhaust port. An exhaust valve may be disposed to admit post-combustion gases to the combustion chamber while an exhaust port pressure in the exhaust port is higher than a combustion chamber pressure in the combustion chamber. The exhaust valve may be reopened while the exhaust port pressure is higher than the combustion chamber pressure, and fuel may be injected by a first fuel injector or a second fuel injector. A purpose for injecting fuel while an exhaust port pressure is higher than a combustion chamber pressure may be to elevate the fuel temperature with the exhaust gas, possibly vaporizing the fuel, and also to mix the fuel with the pre-combustion gases entering through the intake valve. Compression of the fuel and air mixture takes place after the intake and the exhaust valves close, allowing the fuel to autoignite and producing homogenous charge compression ignition (HCCI) combustion. Autoignition may be controlled by, e.g. adjusting EGR, the timing of the intake valve event, the compression ratio, or the inlet manifold temperature.
In a third embodiment a fuel injector may be used to control the start of combustion. A first quantity of fuel may be injected into the exhaust port via a second fuel injector while an exhaust port pressure is higher than a combustion chamber pressure and when an exhaust valve is reopened. A temperature of the first quantity of fuel may be elevated by the heat of the exhaust gases, and the fuel may be vaporized, when the first quantity of fuel mixes with pre-combustion gases entering through the intake port. Compression of the fuel and air mixture takes place when the intake and exhaust valves have closed. The first quantity of fuel, however, is insufficient for auto-ignition to occur. Combustion may not occur until fuel is also injected by a first fuel injector in a quantity sufficient to auto-ignite. Engine-out emissions may be controlled by adjusting, e.g. the quantities of fuel injected by the first and the second injectors, a timing of fuel injection by the first fuel injector, the quantity of EGR, a timing of an inlet valve closing, a compression ratio, or an inlet manifold temperature.